1. Field of the Invention
This invention relates to control of a computerized tape-laying machine for applying a course of composite tape along a machine path, and more particularly to such control in which displacement of the tape from the machine path is minimized by rotating the tape applicator head relative the path in a direction to offset the displacement.
2. Description of the Prior Art
By way of background, a computerized tape-laying machine includes a tape dispensing head positionable and movable in multiple axes under computer control relative to a layup tool or the like so as to apply multiple courses or strips of composite tape material to the layup tool and form thereon parts such as aircraft wings, for example. Typically, the tape head is mounted to a gantry/carriage assembly which moves in a plane to cause the head to move back and forth and side-to-side relative the layup tool. The tape head is also typically movable vertically and rotatably relative the layup tool. As a consequence, the tape head may be caused to move in a plurality of rectilinear and/or rotational axes under control of a computer program by which to apply several plies of composite tape material to the layup tool.
As the tape applicator head moves along the machine path in response to commands from the computer control, a path of composite tape is applied to the layup tool therealong. Ideally, the centerline of the tape path coincides precisely with the machine path. Unfortunately, the tape may shift such that the centerline of the tape path becomes laterally displaced from the machine path, especially where the machine path is not a natural path for the tape. If not corrected, such displacement error could lead to machine shut-down and/or damage to the tape.
To overcome such displacement errors, it is known to periodically provide commands to rotate the tape dispensing head about an axis through the head and intersecting the machine path, such rotation being in a direction to reduce the displacement of the tape from the machine path as the tape applicator head continues to apply tape along the machine path. While such a technique to correct for displacement errors is known to be advantageous, normal operation of the computer controls which implement that technique have introduced drawbacks which limit the effectiveness of such correction. In particular, such correction has been made on a temporal basis such that the tape dispensing head is rotated to correct for displacement error at predetermined or fixed intervals of time.
Making displacement error corrections at predetermined time intervals has been found to be disadvantageous. For example, when the tape applicator head is not moving (at standstill), but is bearing against the layup tool, generating an error correction command after an elapsed period of time may cause a rotational adjustment of the tape applicator head against the tape and layup tool, thereby resulting in damage to the tape. Further, because the speed at which the applicator head is moving along the machine path may vary widely and, thus, tape application speeds may vary widely, selection of the predetermined time interval for displacement correction, i.e., selection of the temporal clock period, does not allow for minimizing tape displacement error uniformly over a wide range of velocities. Thus, selection of the temporal clock period may necessarily require compromise in performance of the tape-laying machine and the product produced thereby.